Coated abrasive articles generally contain an abrasive material, typically in the form of abrasive particles, bonded to a previously made backing by means of one or more adhesive layers. The adhesive layers and abrasive particles are conventionally applied to the backing in separate step(s) after the backing has been formed. Such articles usually take the form of sheets, discs, belts, bands, and the like, which can be adapted to be mounted on pulleys, wheels, or drums. Abrasive articles can be used for sanding, grinding or polishing various surfaces of, for example, steel and other metals, wood, wood-like laminates, plastic, fiberglass, leather, or ceramics.
The backings or substrates used in coated abrasive articles are typically made of paper, polymeric materials, cloth, non-woven materials, vulcanized rubber, or combinations of these materials. Many of these materials provide unacceptable backings for certain applications because they are not of sufficient strength, flexibility, or impact-resistance. In addition, some of these materials age too rapidly which is unacceptable. Furthermore, some of the materials are sensitive to liquids that are used as coolants and cutting fluids. Accordingly, early failure and poor functioning can occur in certain applications.
In a typical manufacturing process, a coated abrasive article is made by feeding a preformed backing in a continuous web form through a series of coating and curing steps wherein binder layers and abrasive particles are applied. The coated web is then converted into a desired construction, such as a sheet, disc, belt or the like. One of the most useful constructions of a coated abrasive article is an endless coated abrasive belt, i.e., a continuous loop of coated abrasive material. In order to form such an endless belt, the web form is typically cut into an elongate strip of a desired width and length. The ends of the elongate strip are then joined together to create a "joint" or a "splice".
Two types of splices are common in endless abrasive belts. These are the "lap" splice and the "butt" splice. For the lap splice, the ends of the elongate strip are doubled such that the top surface with the abrasive coating and the bottom surface of the backing fit together without a significant change in the overall thickness of the belt. This is typically done by removing abrasive particles from the abrasive surface of the strip at one of the ends, and by removing part of the material from the backing of the elongate strip at the other end. The doubled ends are then overlapped and joined adhesively. For the butt splice, the bottom surface of the backing at each end of the elongate strip is coated with an adhesive end overlaid with a strong, thin, tear-resistant, splicing media. Each end for either of these splices may be cut straight or have mating curves of various configurations. Although endless coated abrasive belts containing a splice in the backing are widely used in industry today, these products suffer from some disadvantages which can be attributed to the splice.
For example, the splice is generally thicker than the rest of the coated abrasive belt, even though the methods of splicing generally used involve attempts to minimize this variation in the thickness along the length of the belt. This can lead to a region on the workpiece with a "coarser" surface finish than the remainder of the workpiece, which is highly undesirable, especially in high precision grinding applications. For example, wood with areas having a coarser surface finish will stain darker than the remainder of the wood. Also, the splice can be the weakest area or link in the coated abrasive belt. In extreme cases the splice may break prematurely before full utilization of the coated abrasive belt, which leads not only to waste, but potential hazard. Belts have therefore often been made with laminated liners or backings to give added strength and support. Such belts can be relatively expensive and, under certain conditions, can be subject to separation of the laminated layers.
In addition, abrading machines that utilize a coated abrasive belt can have difficulty properly tracking and aligning the belt because the splice creates a discontinuity in the coated abrasive belt. Furthermore, the spliced area can be undesirably more stiff than the remainder of the belt, and belts including a splice may put undesirable "chatter" marks on the workpiece. Finally, the splice in the belt backing adds considerable expense in the manufacturing process of coated abrasive belts.
Prior references have shown methods for producing endless, seamless abrasive belts. For example, Ball (U.S. Pat. No. 2,404,207) discloses belts produced by a method that utilizes a carrier belt that is rotated around support rolls. A comb removes a carded membrane from a stripper roll to thereby deposit the carded membrane upon the rotating carrier belt. Accordingly, layers of carded membrane are incrementally deposited around a peripheral surface of the carrier belt as the carrier belt is rotated around the support rolls. The carded membrane can be comprised of fibrous materials such that layers of fibrous materials form a web about the carrier belt. A pressure roll is used to compact the web and impregnate the web with an adhesive binder material. Abrasive particles can also be distributed upon the carrier belt through two different control hoppers.
A variation of a butt splice is presented in Dyer (U.S. Pat. No. 4,018,574). Dyer discloses a process for manufacturing an endless coated abrasive article. The process involves inserting a strip of coated abrasive material inside an open-ended cylindrical mold with the abrasive coated surface adjacent to and in contact with an inner peripheral surface of the mold. The strip of coated abrasive material is cut in a shape such that longitudinal edges of the abrasive material abut to form a helical butt joint. A resin composition including a suitable reinforcing material is introduced to the mold after the mold is set in rotation. The rotation of the mold creates centrifugal force which causes the resinous mixture to flow outwardly to thereby distribute the resinous composition uniformly upon the back of the abrasive material. The resin material is then cured to form a layer on the inner periphery of the finished coated abrasive belt. The process results in an endless coated abrasive article that has a helical-shaped seam or splice extending throughout the abrasive material.
PCT International Publication No. WO 93/12911, published Jul. 8, 1993, discloses fiber reinforced polymeric backings and coated abrasives employing same. In producing the backing, the fibers are engulfed by a polymer and the polymer is then solidified or cured, depending on the polymer's chemistry. Abrasive particles are then adhered to the backing by a subsequent resin coating applied to the backing (sometimes referred to as a "make" coating), typically a resole phenolic resin. The abrasive articles and methods of making same described in WO 93/12911 thus require a separate make coating step. Further, the procedures for making the fiber reinforced backings are essentially batch procedures.
It would be advantageous if fiber reinforced coated abrasive articles could be made by eliminating the step of applying a separate make coating to a preformed backing, and if the process of making a coated abrasive having a fiber reinforced backing could be either a batch process or a continuous web process. This could result in significant cost savings.